The invention relates to a method and apparatus for profiling the cure within a pultrusion tool. Monitoring the profile of the degree of cure along the length of a pultrusion tool (die) allows understanding of the cure profile""s response to different processing parameters. Once this understanding is complete and simulations are developed to model the cure profile""s performance, the profile can be used as a process control input. Then the process can be fully automated to insure optimal processing and quality.
Composite materials can be manufactured in many ways, the most economical of which is pultrusion. Pultrusion is used to manufacture constant cross-section material in a continuous process. It is desired to optimize processing to maintain quality and increase line speed to its maximum. Current state of the art includes extensive heat transfer and resin kinetic modeling (see Sumerak, Joseph E., xe2x80x9cPultrusion Die Design Optimization Opportunities Using Thermal Finite Element Analysis,xe2x80x9d The Society of the Plastics Industry, Inc. Feb. 7-9, 1994, session 9-C pp. 1-7). These models are then coupled to process sensors to allow for process control. As Dr. Joseph Sumerak on pultrusion process control has stated: xe2x80x9cThe most critical controls are found in the control of line speed and die temperatures, both of which have primary impact on the state of cure of the composite pultrusion. Sophisticated control scenarios for closed-loop line speed control and PID temperature control provide precision in response to operator setpoints. Unfortunately, however, the ability to continuously detect the degree of cure of the composite for use as a process control parameter does not yet exist. xe2x80x9d Sumerak, Joseph E., xe2x80x9cThe Pultrusion Process for Continuous Automated Manufacture of Engineered Composite Profiles,xe2x80x9d Composites Engineering Handbook, Edited by P. K. Mallick, 1997, Chapter 11, pp. 549-577.
Several attempts at placing pressure, temperature, and dielectric sensors into the die have been made (see Nolet, S. C., xe2x80x9cDevelopment of a Sensor for Continuously Monitoring the Degree of Cure of Composite Materials during Pultrusion,xe2x80x9d Report No.: NSF/ISI-89022. Cable, D., xe2x80x9cEmbedded fiber optic pressure and temperature sensors enable cure monitoring of pultruded composite materials,xe2x80x9d Society of Manufacturing Engineers, Conference on Effective Manufacturing Methods of Pultrusion, Manhattan Beach, Calif., May 9-10, 1990, pp. 6. Fanucci, J. P.; Nolet, S. C.; Koppernaes, C.; Chou, Hsin-Nan, xe2x80x9cThin disposable pressure sensors for composite material process monitoring,xe2x80x9d Society for the Advancement of Material and Process Engineering, 1990, pp. 1205-1219. Methven, J. M.; Katramados, Y., xe2x80x9cIn-line quality monitoring of pultruded profiles using dielectric Measurements,xe2x80x9d Polymers and Polymer Composites, 5, (1), pp. 15-20). The present invention inexpensively, continuously, and easily profiles the degree of cure in the pultrusion die.
An important object of the invention is to provide an improved method and apparatus to determine the degree of cure along the length of a pultrusion die. Advantages of the invention include increased accuracy, increased applicability, and reduced costs.
First, the invention offers considerable increases in accuracy by (1) using a sensor methodology that is not as subject to degradation as dielectric sensors; (2) using an electrical circuit configuration that allows direct measurement across the resin material; and (3) using a series of sensors across cross-sections of a die to monitor the cure profile along the length of the die in different thickness regions; and (4) using a series of sensors that allow the cure profile along the length of the pultrusion tool to be monitored.
Second, the invention offers considerably increased applicability by (1) using a sensor configuration that is easily integrated into the tool; (2) monitoring the degree of cure along the length of the tool; (3) using a sensor material that is easy to integrate into the preform; (4) using a sensor material that is common to composite material construction to therefore prevent any degradation of the properties of the composite material; and (5) using either Alternating Current (AC) or Direct Current (DC).
Finally, the invention offers a considerable cost savings advantage by (1) eliminating expensive sensors; (2) eliminating the need for specialized coating of sensors to extend life; and (3) allowing the process to be optimized and then fully automated.